<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>include block</title>
    <style type="text/css">
        #a,#b{
            width: 100px;
            height: 100px;
            float: left;
            margin-top: 10px;
            border: solid 1px red;
        }
        #b{
            position: relative;
            margin-left: 10px;
        }
        #c,#d{
            width: 50%;
            height: 50%;
            position: absolute;
            left: 50%;
            top: 50%;
        }
        #c{
            background-color: #0F0;
        }
        #d{
            background-color: #00f;
        }
    </style>
</head>
<body>
<div id="a">a
    <div id="c">c</div>
</div>
<div id="b">b
    <div id="d">d</div>
</div>
</body>
</html>